April 24, 2024

Dynamic Sun – Magnetic forces that shape solar phenomena

In drawings and paintings, the sun often appears as a perfect circle of light, projecting its energy equally in all directions. However, if we look closer, we will observe occasional eruptions in specific directions. Solar flares occur when energy stored in the Sun’s magnetic field is suddenly discharged, rapidly heating surrounding matter to millions of degrees. This results in the release of a large amount of energy across the electromagnetic spectrum: from gamma rays to X-rays to radio waves. Although our atmosphere protects us from harmful radiation, when these radiation emissions reach Earth, they can disrupt media broadcasts. But this brings us to an intriguing question – why does the Sun have a magnetic field?

When gas reaches extremely high temperatures, it turns into plasma – an ionized gas state. During the ionization process, electrons are released from gas atoms, leading to the formation of free particles with an electrical charge: negative electrons and nuclei of positive atoms. The laws of electrodynamics teach us that when a charged particle is in motion it generates a magnetic field around it and, conversely, a charged particle within a magnetic field will be propelled by it and create an electric current. In fact, this principle forms the basis of the dynamo generator.

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A simulation of the Parker spacecraft sailing close to the Sun A simulation of the Parker spacecraft sailing close to the Sun

A simulation of the Parker spacecraft sailing close to the Sun

(Illustration: NASA)

The sun is a giant sphere of plasma that rotates on its axis. The temperature of the sun’s surface is lower than the temperature inside it. Temperature differences cause hot matter in deeper layers to rise while cooler matter in outer layers sinks – a process known as convection, which is also responsible for the swirling motion of boiling water in a kettle. The complex movement of charged plasma particles, driven by convection and the Sun’s axial rotation, generates magnetic fields, which in turn affect the movement of charged particles. The complex motion caused by the combination of convection, the Sun’s rotation – which is different at varying speeds along the lines of latitude on its surface – and local magnetic fields contribute to the intricate dynamics of the Sun’s magnetic field. The depth at which the Sun’s magnetic field originates remains a subject of ongoing investigation.

Solar flares typically occur in “active areas,” where the Sun’s magnetic field is especially strong and its shape is distorted. In these areas, “sunspots” often develop, which are similar to dark spots that appear on the surface of the Sun for a brief period and then disappear. In specific areas, the distortion of the magnetic field interrupts the convection of the deeper layers towards the outside, leading to a decrease in temperature and the appearance of darker tones.

A NASA video detailing the changes in the Sun’s magnetic field:

The first documented observation of sunspots dates back to the Chinese “Book of Changes” (I Ching), written more than 2,800 years ago. Starting in the 28th century BC, Chinese astronomers methodically documented sunspots.

The first recorded report of sunspots in the Western world was made by the Greek philosopher Theophrastus, around 300 BC. The first to observe sunspots through a telescope – or at least the first to document it, was the English astronomer Tomas Harriot in December 1610. In 1775, Danish astronomer Christian Horrebow noticed that the number and size of sunspots change on a cycle of a few years. In a paper published in 1801, British astronomer William Herschel claimed to have found a link between the number and shape of sunspots and the temperature measured at the Earth’s surface, and even between the number of sunspots and wheat prices in Great Britain. Brittany. However, these claims were later refuted. In 1843, the German astronomer Heinrich Schwabe presented a clear cycle in the average number of sunspots, while in 1852 the Swiss astronomer Rudolf Wolf established a numbering system for solar cycles, dating back to the mid-18th century, with the cycle that began in 1755 considered as the first cycle of the count. The average duration of a solar cycle is approximately eleven years and is defined as the period between two periods of low solar activity.

By analyzing the frequency of the carbon-14 isotope in tree rings, scientists in 2004 successfully reconstructed solar activity levels over the past 11,400 years, since the last ice age. The researchers found that for ninety percent of this extended period, the level of solar activity was lower than that observed between the 1940s and the early 2000s, and almost all previous periods of increased activity were shorter than this period. . In the last solar cycle, cycle number twenty-four, which lasted from December 2008 to December 2019, solar activity was significantly lower than what was considered usual in recent decades, similar to levels documented between the end of the 19th century and the beginning of the 20th century.

Is there a link between solar activity levels and global warming on Earth? Most researchers believe that the Sun’s contribution to the warming trend observed in recent decades is negligible. For example, although the Earth has experienced gradual warming since the mid-20th century, the intensity of solar radiation reaching us has remained relatively stable since at least the mid-19th century. Furthermore, if solar activity were the main driver of global warming, we would expect warming in all layers of the atmosphere, while the upper atmosphere actually shows a cooling trend.

In addition to flares and sunspots, the activity of the Sun’s magnetic field can also lead to coronal mass ejections. The corona is a type of very hot aura that surrounds the Sun, composed mainly of ionized hydrogen. Due to the high temperature of the corona, it continually releases charged particles into space, creating a phenomenon known as “solar wind”. These charged particles are attracted to Earth’s magnetic poles and can become trapped in Earth’s magnetic field near the poles. When these charged particles collide with molecules in the upper layers of the atmosphere, typical light is emitted, creating the phenomenon we know as the aurora borealis (Aurora Borealis).

When the Sun’s magnetic activity intensifies the solar wind, it can lead to a geomagnetic storm – a temporary disturbance in Earth’s magnetic field. In extreme cases, such storms can disrupt the operations of satellites, high-voltage power lines, media transmissions, radar and navigation systems, and more.

Thanks to Earth’s atmosphere and magnetosphere, life on Earth is relatively protected from the effects of geomagnetic storms. However, astronauts or individuals flying at high altitudes outside of this protective enclosure or in its surroundings may suffer serious medical implications, such as the formation of mutations that lead to cancer, after exposure to geomagnetic storms. Some argue that such storms also affect animals that depend on Earth’s magnetic field for navigation and migration, although research in this area is still in its infancy.

The current solar cycle, number twenty-five, began in December 2019 and is predicted to last until 2030. Although most projections anticipate that it will be a relatively weak cycle, similar to the previous one, observations from its first three years suggest higher values a -expected levels of activity, although still lower than the cycles that occurred in the 20th century. Thus, for example, two remarkably strong eruptions occurred during the recent month of August. However, peak solar activity is still ahead of us and is predicted to occur in late 2024 or during 2025.

Although researchers in the field generally agree that solar activity levels have little effect on global warming, solar cycles can still affect our daily lives through disruptions to communications and navigation systems and damage to high-voltage power lines. In addition to its practical significance, the study of solar activity has great theoretical importance. Continued observation and monitoring of the Sun and its magnetic activity will deepen our understanding of the mechanisms underlying the formation and development of the Sun’s magnetic field – and that of other stars in the Universe.

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